For moderate and high-loss hearing aid users with vented earmolds, vent dimensions are typically chosen to provide an acceptable balance between acoustic feedback and the occlusion effect. Acoustic feedback occurs when amplified sound propagates from the ear canal, outward through the vent, and into the hearing aid microphone inlet thereby causing an audible and annoying whistle to the user. In general, this acoustic feedback whistling occurs at higher frequencies, typically above 1 kHz. The occlusion effect can be described as an unnatural perception of one's own voice, and occurs when a hearing aid user's earmold is insufficiently occluded thereby causing an accentuation of low-frequency speech energy in the ear canal that is typically perceived as a boominess. Although a wider, more open vent has been successful in prior art in providing the user with a more natural perception of their own voice, such a venting scheme makes the hearing aid more susceptible to acoustic feedback.
Thus, there is a need in the art for a venting scheme that allows the low-frequency speech energy to escape the ear canal more readily and attenuates acoustic feedback at higher frequencies. Compared to a single vent, dual vents configured as an acoustic filter address both these goals more robustly.